/* crypto/dsa/dsa_ossl.c */

/* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)

 * All rights reserved.

 *

 * This package is an SSL implementation written

 * by Eric Young (eay@cryptsoft.com).

 * The implementation was written so as to conform with Netscapes SSL.

 *

 * This library is free for commercial and non-commercial use as long as

 * the following conditions are aheared to.  The following conditions

 * apply to all code found in this distribution, be it the RC4, RSA,

 * lhash, DES, etc., code; not just the SSL code.  The SSL documentation

 * included with this distribution is covered by the same copyright terms

 * except that the holder is Tim Hudson (tjh@cryptsoft.com).

 *

 * Copyright remains Eric Young's, and as such any Copyright notices in

 * the code are not to be removed.

 * If this package is used in a product, Eric Young should be given attribution

 * as the author of the parts of the library used.

 * This can be in the form of a textual message at program startup or

 * in documentation (online or textual) provided with the package.

 *

 * Redistribution and use in source and binary forms, with or without

 * modification, are permitted provided that the following conditions

 * are met:

 * 1. Redistributions of source code must retain the copyright

 *    notice, this list of conditions and the following disclaimer.

 * 2. Redistributions in binary form must reproduce the above copyright

 *    notice, this list of conditions and the following disclaimer in the

 *    documentation and/or other materials provided with the distribution.

 * 3. All advertising materials mentioning features or use of this software

 *    must display the following acknowledgement:

 *    "This product includes cryptographic software written by

 *     Eric Young (eay@cryptsoft.com)"

 *    The word 'cryptographic' can be left out if the rouines from the library

 *    being used are not cryptographic related :-).

 * 4. If you include any Windows specific code (or a derivative thereof) from

 *    the apps directory (application code) you must include an acknowledgement:

 *    "This product includes software written by Tim Hudson (tjh@cryptsoft.com)"

 *

 * THIS SOFTWARE IS PROVIDED BY ERIC YOUNG ``AS IS'' AND

 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE

 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE

 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE

 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL

 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS

 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)

 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT

 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY

 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF

 * SUCH DAMAGE.

 *

 * The licence and distribution terms for any publically available version or

 * derivative of this code cannot be changed.  i.e. this code cannot simply be

 * copied and put under another distribution licence

 * [including the GNU Public Licence.]

 */

/* Original version from Steven Schoch <schoch@sheba.arc.nasa.gov> */

#include <stdio.h>

#include "cryptlib.h"

#include <openssl/bn.h>

#include <openssl/sha.h>

#include <openssl/dsa.h>

#include <openssl/rand.h>

#include <openssl/asn1.h>

static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa);

static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,

                          BIGNUM **rp);

static int dsa_do_verify(const unsigned char *dgst, int dgst_len,

                         DSA_SIG *sig, DSA *dsa);

static int dsa_init(DSA *dsa);

static int dsa_finish(DSA *dsa);

static DSA_METHOD openssl_dsa_meth = {

    "OpenSSL DSA method",

    dsa_do_sign,

    dsa_sign_setup,

    dsa_do_verify,

    NULL,                       /* dsa_mod_exp, */

    NULL,                       /* dsa_bn_mod_exp, */

    dsa_init,

    dsa_finish,

    0,

    NULL,

    NULL,

    NULL

};

/*-

 * These macro wrappers replace attempts to use the dsa_mod_exp() and

 * bn_mod_exp() handlers in the DSA_METHOD structure. We avoid the problem of

 * having a the macro work as an expression by bundling an "err_instr". So;

 *

 *     if (!dsa->meth->bn_mod_exp(dsa, r,dsa->g,&k,dsa->p,ctx,

 *                 dsa->method_mont_p)) goto err;

 *

 * can be replaced by;

 *

 *     DSA_BN_MOD_EXP(goto err, dsa, r, dsa->g, &k, dsa->p, ctx,

 *                 dsa->method_mont_p);

 */

#define DSA_MOD_EXP(err_instr,dsa,rr,a1,p1,a2,p2,m,ctx,in_mont) \

        do { \

        int _tmp_res53; \

        if ((dsa)->meth->dsa_mod_exp) \

                _tmp_res53 = (dsa)->meth->dsa_mod_exp((dsa), (rr), (a1), (p1), \

                                (a2), (p2), (m), (ctx), (in_mont)); \

        else \

                _tmp_res53 = BN_mod_exp2_mont((rr), (a1), (p1), (a2), (p2), \

                                (m), (ctx), (in_mont)); \

        if (!_tmp_res53) err_instr; \

        } while(0)

#define DSA_BN_MOD_EXP(err_instr,dsa,r,a,p,m,ctx,m_ctx) \

        do { \

        int _tmp_res53; \

        if ((dsa)->meth->bn_mod_exp) \

                _tmp_res53 = (dsa)->meth->bn_mod_exp((dsa), (r), (a), (p), \

                                (m), (ctx), (m_ctx)); \

        else \

                _tmp_res53 = BN_mod_exp_mont((r), (a), (p), (m), (ctx), (m_ctx)); \

        if (!_tmp_res53) err_instr; \

        } while(0)

const DSA_METHOD *DSA_OpenSSL(void)

{

    return &openssl_dsa_meth;

}

static DSA_SIG *dsa_do_sign(const unsigned char *dgst, int dlen, DSA *dsa)

{

    BIGNUM *kinv = NULL, *r = NULL, *s = NULL;

    BIGNUM m;

    BIGNUM xr;

    BN_CTX *ctx = NULL;

    int reason = ERR_R_BN_LIB;

    DSA_SIG *ret = NULL;

    int noredo = 0;

    BN_init(&m);

    BN_init(&xr);

    if (!dsa->p || !dsa->q || !dsa->g) {

        reason = DSA_R_MISSING_PARAMETERS;

        goto err;

    }

    s = BN_new();

    if (s == NULL)

        goto err;

    ctx = BN_CTX_new();

    if (ctx == NULL)

        goto err;

 redo:

    if ((dsa->kinv == NULL) || (dsa->r == NULL)) {

        if (!DSA_sign_setup(dsa, ctx, &kinv, &r))

            goto err;

    } else {

        kinv = dsa->kinv;

        dsa->kinv = NULL;

        r = dsa->r;

        dsa->r = NULL;

        noredo = 1;

    }

    if (dlen > BN_num_bytes(dsa->q))

        /*

         * if the digest length is greater than the size of q use the

         * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,

         * 4.2

         */

        dlen = BN_num_bytes(dsa->q);

    if (BN_bin2bn(dgst, dlen, &m) == NULL)

        goto err;

    /* Compute  s = inv(k) (m + xr) mod q */

    if (!BN_mod_mul(&xr, dsa->priv_key, r, dsa->q, ctx))

        goto err;               /* s = xr */

    if (!BN_add(s, &xr, &m))

        goto err;               /* s = m + xr */

    if (BN_cmp(s, dsa->q) > 0)

        if (!BN_sub(s, s, dsa->q))

            goto err;

    if (!BN_mod_mul(s, s, kinv, dsa->q, ctx))

        goto err;

    /*

     * Redo if r or s is zero as required by FIPS 186-3: this is very

     * unlikely.

     */

    if (BN_is_zero(r) || BN_is_zero(s)) {

        if (noredo) {

            reason = DSA_R_NEED_NEW_SETUP_VALUES;

            goto err;

        }

        goto redo;

    }

    ret = DSA_SIG_new();

    if (ret == NULL)

        goto err;

    ret->r = r;

    ret->s = s;

 err:

    if (ret == NULL) {

        DSAerr(DSA_F_DSA_DO_SIGN, reason);

        BN_free(r);

        BN_free(s);

    }

    if (ctx != NULL)

        BN_CTX_free(ctx);

    BN_clear_free(&m);

    BN_clear_free(&xr);

    if (kinv != NULL)           /* dsa->kinv is NULL now if we used it */

        BN_clear_free(kinv);

    return (ret);

}

static int dsa_sign_setup(DSA *dsa, BN_CTX *ctx_in, BIGNUM **kinvp,

                          BIGNUM **rp)

{

    BN_CTX *ctx;

    BIGNUM k, kq, *K, *kinv = NULL, *r = NULL;

    BIGNUM l, m;

    int ret = 0;

    int q_bits;

    if (!dsa->p || !dsa->q || !dsa->g) {

        DSAerr(DSA_F_DSA_SIGN_SETUP, DSA_R_MISSING_PARAMETERS);

        return 0;

    }

    BN_init(&k);

    BN_init(&kq);

    BN_init(&l);

    BN_init(&m);

    if (ctx_in == NULL) {

        if ((ctx = BN_CTX_new()) == NULL)

            goto err;

    } else

        ctx = ctx_in;

    if ((r = BN_new()) == NULL)

        goto err;

    /* Preallocate space */

    q_bits = BN_num_bits(dsa->q);

    if (!BN_set_bit(&k, q_bits)

        || !BN_set_bit(&l, q_bits)

        || !BN_set_bit(&m, q_bits))

        goto err;

    /* Get random k */

    do

        if (!BN_rand_range(&k, dsa->q))

            goto err;

    while (BN_is_zero(&k));

    if ((dsa->flags & DSA_FLAG_NO_EXP_CONSTTIME) == 0) {

        BN_set_flags(&k, BN_FLG_CONSTTIME);

    }

    if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {

        if (!BN_MONT_CTX_set_locked(&dsa->method_mont_p,

                                    CRYPTO_LOCK_DSA, dsa->p, ctx))

            goto err;

    }

    /* Compute r = (g^k mod p) mod q */

    if ((dsa->flags & DSA_FLAG_NO_EXP_CONSTTIME) == 0) {

        /*

         * We do not want timing information to leak the length of k, so we

         * compute G^k using an equivalent scalar of fixed bit-length.

         *

         * We unconditionally perform both of these additions to prevent a

         * small timing information leakage.  We then choose the sum that is

         * one bit longer than the modulus.

         *

         * TODO: revisit the BN_copy aiming for a memory access agnostic

         * conditional copy.

         */

        if (!BN_add(&l, &k, dsa->q)

            || !BN_add(&m, &l, dsa->q)

            || !BN_copy(&kq, BN_num_bits(&l) > q_bits ? &l : &m))

            goto err;

        BN_set_flags(&kq, BN_FLG_CONSTTIME);

        K = &kq;

    } else {

        K = &k;

    }

    DSA_BN_MOD_EXP(goto err, dsa, r, dsa->g, K, dsa->p, ctx,

                   dsa->method_mont_p);

    if (!BN_mod(r, r, dsa->q, ctx))

        goto err;

    /* Compute  part of 's = inv(k) (m + xr) mod q' */

    if ((kinv = BN_mod_inverse(NULL, &k, dsa->q, ctx)) == NULL)

        goto err;

    if (*kinvp != NULL)

        BN_clear_free(*kinvp);

    *kinvp = kinv;

    kinv = NULL;

    if (*rp != NULL)

        BN_clear_free(*rp);

    *rp = r;

    ret = 1;

 err:

    if (!ret) {

        DSAerr(DSA_F_DSA_SIGN_SETUP, ERR_R_BN_LIB);

        if (r != NULL)

            BN_clear_free(r);

    }

    if (ctx_in == NULL)

        BN_CTX_free(ctx);

    BN_clear_free(&k);

    BN_clear_free(&kq);

    BN_clear_free(&l);

    BN_clear_free(&m);

    return ret;

}

static int dsa_do_verify(const unsigned char *dgst, int dgst_len,

                         DSA_SIG *sig, DSA *dsa)

{

    BN_CTX *ctx;

    BIGNUM u1, u2, t1;

    BN_MONT_CTX *mont = NULL;

    int ret = -1, i;

    if (!dsa->p || !dsa->q || !dsa->g) {

        DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MISSING_PARAMETERS);

        return -1;

    }

    i = BN_num_bits(dsa->q);

    /* fips 186-3 allows only different sizes for q */

    if (i != 160 && i != 224 && i != 256) {

        DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_BAD_Q_VALUE);

        return -1;

    }

    if (BN_num_bits(dsa->p) > OPENSSL_DSA_MAX_MODULUS_BITS) {

        DSAerr(DSA_F_DSA_DO_VERIFY, DSA_R_MODULUS_TOO_LARGE);

        return -1;

    }

    BN_init(&u1);

    BN_init(&u2);

    BN_init(&t1);

    if ((ctx = BN_CTX_new()) == NULL)

        goto err;

    if (BN_is_zero(sig->r) || BN_is_negative(sig->r) ||

        BN_ucmp(sig->r, dsa->q) >= 0) {

        ret = 0;

        goto err;

    }

    if (BN_is_zero(sig->s) || BN_is_negative(sig->s) ||

        BN_ucmp(sig->s, dsa->q) >= 0) {

        ret = 0;

        goto err;

    }

    /*

     * Calculate W = inv(S) mod Q save W in u2

     */

    if ((BN_mod_inverse(&u2, sig->s, dsa->q, ctx)) == NULL)

        goto err;

    /* save M in u1 */

    if (dgst_len > (i >> 3))

        /*

         * if the digest length is greater than the size of q use the

         * BN_num_bits(dsa->q) leftmost bits of the digest, see fips 186-3,

         * 4.2

         */

        dgst_len = (i >> 3);

    if (BN_bin2bn(dgst, dgst_len, &u1) == NULL)

        goto err;

    /* u1 = M * w mod q */

    if (!BN_mod_mul(&u1, &u1, &u2, dsa->q, ctx))

        goto err;

    /* u2 = r * w mod q */

    if (!BN_mod_mul(&u2, sig->r, &u2, dsa->q, ctx))

        goto err;

    if (dsa->flags & DSA_FLAG_CACHE_MONT_P) {

        mont = BN_MONT_CTX_set_locked(&dsa->method_mont_p,

                                      CRYPTO_LOCK_DSA, dsa->p, ctx);

        if (!mont)

            goto err;

    }

    DSA_MOD_EXP(goto err, dsa, &t1, dsa->g, &u1, dsa->pub_key, &u2, dsa->p,

                ctx, mont);

    /* BN_copy(&u1,&t1); */

    /* let u1 = u1 mod q */

    if (!BN_mod(&u1, &t1, dsa->q, ctx))

        goto err;

    /*

     * V is now in u1.  If the signature is correct, it will be equal to R.

     */

    ret = (BN_ucmp(&u1, sig->r) == 0);

 err:

    if (ret < 0)

        DSAerr(DSA_F_DSA_DO_VERIFY, ERR_R_BN_LIB);

    if (ctx != NULL)

        BN_CTX_free(ctx);

    BN_free(&u1);

    BN_free(&u2);

    BN_free(&t1);

    return (ret);

}

static int dsa_init(DSA *dsa)

{

    dsa->flags |= DSA_FLAG_CACHE_MONT_P;

    return (1);

}

static int dsa_finish(DSA *dsa)

{

    if (dsa->method_mont_p)

        BN_MONT_CTX_free(dsa->method_mont_p);

    return (1);

}